This invention relates to a device for suppressing a subcarrier component remaining in the output signal of a balanced modulator included, for example, in a stereophonic modulation circuit for forming a sub-channel of a FM stereophonic composite signal.
As shown, for example, in pages 66 to 70 of "BROADCASTERS" edited by Nippon Hoso Kyokai (Japanese Broadcast Association) and published by Nippon Hoso Shuppan Kyokai (Japanese Broadcast Publishing Association) on Apr. 20, 1983, in a stereophonic modulation circuit, left and right signals L and R are matrixed to form sum and difference signals L+R and L-R which are separately processed and then mixed by a mixer amplifier to form a stereophonic composite signal. The L-R signal processing channel includes a balanced modulator for modulating a 38 KHz subcarrier wave from a subcarrier generator with the L-R signal to form a frequency-modulated (FM) difference signal. This output signal of the balanced modulator generally includes a substantial amount of remanent subcarrier component which is to be removed or suppressed by a band-pass filter as shown in the above-cited reference. For complete removal of such subcarrier component, however, it has been necessary to use a complicated expensive filter circuit.